While the influences of genes and environments on cognitive development have traditionally been viewed as independent, if not competing, forces, there is an emerging theoretical consensus that cognitive development results from interactions between genes and cumulative environmental experiences. However, while the little gene-by-environment (GxE) interaction research on cognitive development that has been conducted to date has primarily focused on children's experiences during grade school, very recent work suggests that GxE on cognitive development emerges much earlier - as early as 2 years of age. In low socioeconomic status homes, genetic influences on infant cognitive function approach zero, whereas in high socioeconomic status homes, genes account for approximately 50% of the variation in infant cognitive function. Using data on approximately 800 pairs of fraternal and identical twins that were collected as part of the Early Childhood Longitudinal Study - Birth Cohort (ECLS-B), this project will take steps to clarify GxE interaction effects on early cognitive development in three important respects. Aim 1: Identify Parent Behaviors that Moderate Genetic Influences on Infant Cognitive Function. For the first aim, this project will examine the roles that parent behaviors play in moderating genetic influences on infant cognitive function. A guiding hypothesis is that parental responsiveness to infant cues is crucial to the expression of genetic potential for early cognitive development. Aim 2: Understand the Association Between Infant Behaviors and Infant Cognitive Function. For the second aim, this project will examine the genetic and environmental bases for the relations between infant knowledge-seeking behaviors and infant cognitive function, and whether socioeconomic advantage and parental responsiveness moderate these relations. This will help to determine whether GxE interactions on infant cognitive functions can be accounted for by differences in levels of support of children's knowledge seeking behaviors. Aim 3: Link GxE Affects on Cognitive Function with School Entry Skills in Kindergarten. For the final aim, this project will examine the extent to which GxE effects on infant cognitive function extend to school entry skills (mathematics, reading, and attentional skills) measured at 4 and 5 years, and whether new GxE effects independent of previous GxE effects emerge at school entry. Identifying early life experiences that facilitate the expression of genes for healthy cognitive development and school readiness will support NICHD's mission to ensure that all children have their chance to achieve their full potential for healthy and productive lives.